The blades and vanes which are commonly used in the turbine section of modern gas turbine engines are typically made of nickel and cobalt based superalloys. The composition of the superalloys are generally tailored to provide a desirable combination of mechanical strength and resistance to environmental degradation (e.g., oxidation and hot corrosion). Coatings are often used to increase the level of oxidation and hot corrosion resistance, to allow the components made from such superalloys to be used for long periods of time before they need to be replaced or repaired.
Such protective coatings are typically of two different types overlay coatings and diffusion coatings. Representative of the overlay coatings are the MCrAlY family of coatings, as described in U.S. Pat. Nos. 3,928,026 to Hecht et al and U.S Pat. No. Re. 32,121 to Gupta et al. Overlay coatings are applied by physical vapor deposition techniques such as plasma spraying or electron beam evaporation techniques. Representative of the diffusion coatings are the aluminide coatings described in U.S. Pat. Nos. 3,544,348 to Boone et al and 4,132,816 to Benden et al.
In some circumstances, coatings are applied to only certain surfaces of the engine component. In the case of a turbine blade, it is sometimes necessary to keep the root portion of the blade free of coating. To accomplish such selective coating application, masks are used to protect or shield such surfaces Masks used in the diffusion coating industry are described in, for example, U.S. Pat. Nos. 3,764,371, 3,785,854, 3,801,357, to Baldi; 3,904,789 to Speirs et al; and 4,128,522 to Elam; the contents of each of these patents are incorporated by reference. While such types of masks are generally considered to be useful, their application is a time-consuming and labor intensive process. Accordingly, improvements in diffusion coating masks and their method of application are desired, and in particular, a mask which is quickly and easily applied is needed for the diffusion coating industry.